image: Convert to use fdt_for_each_subnode macro

Use fdt_for_each_subnode macro to simplify the code a bit.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Acked-by: Simon Glass <sjg@chromium.org>
diff --git a/common/image-sig.c b/common/image-sig.c
index 2c9f0cd..eda5e13 100644
--- a/common/image-sig.c
+++ b/common/image-sig.c
@@ -212,9 +212,7 @@
 	int ret;
 
 	/* Process all hash subnodes of the component image node */
-	for (noffset = fdt_first_subnode(fit, image_noffset);
-	     noffset >= 0;
-	     noffset = fdt_next_subnode(fit, noffset)) {
+	fdt_for_each_subnode(fit, noffset, image_noffset) {
 		const char *name = fit_get_name(fit, noffset, NULL);
 
 		if (!strncmp(name, FIT_SIG_NODENAME,
@@ -262,9 +260,7 @@
 		return 0;
 	}
 
-	for (noffset = fdt_first_subnode(sig_blob, sig_node);
-	     noffset >= 0;
-	     noffset = fdt_next_subnode(sig_blob, noffset)) {
+	fdt_for_each_subnode(sig_blob, noffset, sig_node) {
 		const char *required;
 		int ret;
 
@@ -397,9 +393,7 @@
 	int ret;
 
 	/* Process all hash subnodes of the component conf node */
-	for (noffset = fdt_first_subnode(fit, conf_noffset);
-	     noffset >= 0;
-	     noffset = fdt_next_subnode(fit, noffset)) {
+	fdt_for_each_subnode(fit, noffset, conf_noffset) {
 		const char *name = fit_get_name(fit, noffset, NULL);
 
 		if (!strncmp(name, FIT_SIG_NODENAME,
@@ -444,9 +438,7 @@
 		return 0;
 	}
 
-	for (noffset = fdt_first_subnode(sig_blob, sig_node);
-	     noffset >= 0;
-	     noffset = fdt_next_subnode(sig_blob, noffset)) {
+	fdt_for_each_subnode(sig_blob, noffset, sig_node) {
 		const char *required;
 		int ret;